JP5428788B2 - Receiving device, receiving method, and receiving program - Google Patents

Description

  The present invention relates to a receiving device, a receiving method, and a receiving program.

  In wireless communication, in particular, in the case of broadband transmission, in addition to the path received in advance, there is a path that arrives with a delay, such as through reflection from an obstacle such as a building or a mountain, and intersymbol interference ( ISI: Inter Symbol Interference (ISI). An environment in which a plurality of paths arrives in this way is called a multipath environment. For example, Orthogonal Frequency Division Multiplexing (OFDM), Orthogonal Frequency Division Multiple Access (OFDMA), MC-CDM (Multi Code Multiplexing), MC-CDM (Multi Code Multiplexing) In multi-carrier transmission, a guard interval (GI: Guard Interval) is added to a multi-carrier time domain signal to prevent ISI from occurring in a delay path within the GI. Therefore, if the GI length is set appropriately, good transmission quality that is not affected by ISI can be realized. However, when the receiving apparatus moves at a high speed, propagation path fluctuation in one OFDM symbol becomes large, and inter-carrier interference (ICI: Inter Carrier Interference) occurs. Such an environment is called a high-speed fading environment. ICI significantly degrades reception performance.

  Non-Patent Document 1 describes turbo ICI canceller technology. Specifically, Non-Patent Document 1 suppresses ICI by generating an ICI replica from a bit log likelihood ratio (LLR) of an error correction decoding result and removing the generated replica from the received signal. In addition, it is described that ICI removal residual suppression and optimum detection are performed on a signal remaining after removal.

Masafumi Ito, Satoshi Suyama, Kazuhiko Fukawa, Hiroshi Suzuki, "OFDM turbo interference cancellation reception for scattered pilot signals to remove ICI due to fast fading", IEICE Technical Report, RCS 2003-74, July 2003

However, in the technique of Non-Patent Document 1, since the optimum detection is performed for each subcarrier, the calculation amount increases. Specifically, in the technique of Non-Patent Document 1, the order of the number of multiplications of detection processing for each subcarrier is O (N) (N is the number of FFT points, that is, the order of the number of FFT points). There was a problem of ordering O (N ² ). Further, the technique of Non-Patent Document 1 has a problem that it takes O (N ² log ₂ N) multiplications to generate an optimum detection filter, and a large amount of memory is required to store them. It was.
As described above, the conventional technique has a drawback in that the amount of calculation increases when information is detected from a received signal in a fast fading environment where a delay path exists.

  The present invention has been made in view of the above points, and a receiving apparatus, a receiving method, and a receiving apparatus capable of preventing an increase in calculation amount when detecting information from a received signal in a fast fading environment where a delay path exists. Provide a receiving program.

(1) The present invention has been made in order to solve the above-described problems. In the receiving apparatus that demodulates information from a received signal, the present invention demodulates a propagation path estimation unit that estimates a propagation path estimated value. A symbol replica generation unit that generates a symbol replica that is a modulation symbol of information, a signal extraction unit that extracts each subcarrier component of the received signal from which interference is removed, based on the propagation path estimation value and the symbol replica; And a demodulator that demodulates the signal of each subcarrier component extracted by the signal extractor.
According to the above configuration, the receiving apparatus extracts each subcarrier component of the received signal from which the delayed wave is removed, and demodulates the extracted signal of each subcarrier component, so that an increase in the amount of calculation can be prevented.

  (2) Further, according to the present invention, in the reception apparatus, the signal extraction unit generates a reception signal replica that is a replica of the reception signal in the time domain based on the propagation path estimation value and the symbol replica. A subtracting unit that subtracts the received signal replica from the received signal, a time frequency converting unit that converts a signal subtracted by the subtracting unit into a frequency domain signal, the propagation path estimation value, and the symbol replica A restoration unit that generates a replica signal of a desired signal based on the above, adds the replica signal of the desired signal to the frequency domain signal converted by the time-frequency conversion unit, and extracts each subcarrier component of the received signal And.

  (3) Further, in the reception device according to the present invention, the restoration unit extracts a subcarrier component of the frequency domain signal converted by the time-frequency conversion unit, and extracts the subcarrier component signal. The subcarrier component of the replica signal of the desired signal is added.

  (4) Further, in the reception device according to the present invention, the restoration unit extracts a subcarrier component of the frequency domain signal converted by the time-frequency conversion unit, and extracts the subcarrier component signal. The subcarrier component of the replica signal of the desired signal, which is a subcarrier component close to the subcarrier, is added.

  (5) Further, the present invention is characterized in that, in the above-described receiving apparatus, the receiving apparatus includes a plurality of antennas, and the receiving apparatus performs MIMO transmission scheme communication with the transmitting apparatus.

  (6) Further, the present invention is characterized in that, in the above-described receiving apparatus, the demodulator performs MIMO separation based on the propagation path estimation value.

  (7) In the reception device according to the present invention, the reception device receives, as the reception signal, a stream signal that is a signal sequence transmitted from each of a plurality of antennas included in the transmission device. An extracting unit that generates a received signal replica that is a replica of the received signal in the time domain based on the propagation path estimation value and the symbol replica; and a subtracter that subtracts the received signal replica from the received signal A time frequency conversion unit that converts the signal subtracted by the subtraction unit into a frequency domain signal, and generates a replica signal of a desired signal based on the propagation path estimation value and the symbol replica, and the time frequency conversion A restoration unit that adds a replica signal of the desired signal to the frequency domain signal converted by the unit and extracts each subcarrier component of the received signal; The restoration unit extracts a subcarrier component of the frequency domain signal converted by the time-frequency conversion unit, and extracts the subcarrier component of the replica signal of the desired signal from the extracted subcarrier component signal. Of these, a desired stream component is added.

  (8) Further, in the reception device according to the present invention, the reception device receives, as the reception signal, a stream signal that is a signal sequence transmitted from each of a plurality of antennas included in the transmission device. An extracting unit that generates a received signal replica that is a replica of the received signal in the time domain based on the propagation path estimation value and the symbol replica; and a subtracter that subtracts the received signal replica from the received signal A time frequency conversion unit that converts the signal subtracted by the subtraction unit into a frequency domain signal, and generates a replica signal of a desired signal based on the propagation path estimation value and the symbol replica, and the time frequency conversion A restoration unit that adds a replica signal of the desired signal to the frequency domain signal converted by the unit and extracts each subcarrier component of the received signal; The restoration unit extracts a subcarrier component of the frequency domain signal converted by the time-frequency conversion unit, and extracts the subcarrier component of the replica signal of the desired signal from the extracted subcarrier component signal. All the stream components are added.

  (9) Further, the present invention is characterized in that, in the above receiver, the demodulator demodulates the signal based on a minimum mean square error criterion.

  (10) Further, according to the present invention, in the receiving method in the receiving device that demodulates information from the received signal, the propagation path estimation unit demodulates the first process in which the propagation path estimation value is estimated, and the symbol replica generation unit demodulates. A second step of generating a symbol replica that is a modulation symbol of information, and a signal extraction unit extracts each subcarrier component of the received signal from which interference is removed based on the propagation path estimation value and the symbol replica The receiving method is characterized in that it has a third step and a fourth step in which the demodulator demodulates the signal of each subcarrier component extracted in the third step.

  (11) Further, the present invention provides a computer of a receiving apparatus that demodulates information from a received signal, a propagation path estimation means that estimates a propagation path estimation value, and a symbol replica generation that generates a symbol replica that is a modulation symbol of the demodulated information. Means for extracting each subcarrier component of the received signal from which interference has been removed based on the propagation path estimation value and the symbol replica, and demodulating the signal of each subcarrier component extracted by the signal extraction means A receiving program that functions as a demodulating means.

  According to the present invention, it is possible to prevent an increase in calculation amount when detecting information from a received signal in a fast fading environment where a delay path exists in a wireless communication receiving apparatus.

1 is a conceptual diagram of a communication system according to a first embodiment of the present invention. It is a schematic block diagram which shows the structure of the transmitter which concerns on this embodiment. It is a schematic block diagram which shows the structure of the receiver which concerns on this embodiment. It is the schematic which shows an example of the received signal which concerns on this embodiment. It is a flowchart which shows operation | movement of the receiver which concerns on this embodiment. It is the schematic which shows an example of the simulation conditions of the communication system which concerns on this embodiment. It is the schematic which shows an example of the simulation result of the communication system which concerns on this embodiment. It is a schematic block diagram which shows the structure of the receiver which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows operation | movement of the receiver which concerns on this embodiment. It is a schematic block diagram which shows the structure of the transmitter which concerns on the 3rd Embodiment of this invention. It is a schematic block diagram which shows the structure of the receiver which concerns on this embodiment. It is a schematic block diagram which shows the structure of the received signal replica production | generation part which concerns on this embodiment. It is a flowchart which shows operation | movement of the receiver which concerns on this embodiment.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a conceptual diagram of a communication system according to the first embodiment of the present invention.
In this figure, the communication system includes a transmission apparatus A and a reception apparatus B. This figure shows that D + 1 (D = 3 in FIG. 1) propagation paths (also called paths) d (d = 0, 1, 2,. .., D indicates that the data is received by the receiving device B via D). Note that d is numbered in ascending order in the order of short propagation paths (in order of the arrival time of signals through the propagation path) (d is referred to as a propagation path number). D indicates the maximum propagation path number. For example, when D = 3, there are 4 propagation paths.
Hereinafter, in the present embodiment, the transmission device A is referred to as a transmission device a1, and the reception device B is referred to as a reception device b1.

<About the configuration of the transmission device a1>
FIG. 2 is a schematic block diagram illustrating a configuration of the transmission device a1 according to the present embodiment. In this figure, the transmission device a1 includes a pilot generation unit a101, a coding unit a102, a modulation unit a103, a mapping unit a104, an IFFT unit a105, a GI insertion unit a106, a transmission unit a107, and a transmission antenna unit a108. .

The pilot generation unit a101 generates a pilot signal in which the receiving device b1 stores in advance the amplitude value of the waveform (or the signal sequence), and outputs the pilot signal to the mapping unit a104.
The encoding unit a102 encodes information bits to be transmitted to the receiving apparatus b1 using an error correction code such as a convolutional code, a turbo code, and an LDPC (Low Density Parity Check) code, and encodes the encoded bits. Is generated. The encoding unit a102 outputs the generated encoded bits to the modulating unit a103.
The modulation unit a103 modulates the coded bits input from the coding unit a102 using a modulation method such as PSK (Phase Shift Keying) or QAM (Quadrature Amplitude Modulation). Generate a symbol. Modulation section a103 outputs the generated modulation symbol to mapping section a104.

The mapping unit a104 maps the pilot signal input from the pilot generation unit a101 and the modulation symbol input from the modulation unit a103 to a resource (time-frequency band) based on predetermined mapping information, and performs frequency domain And the generated frequency domain signal is output to the IFFT unit a105. Note that a resource is a unit in which a modulation symbol is arranged, which is composed of one subcarrier and one later-described FFT interval in a frame transmitted by the transmission apparatus a1. Also, the mapping information is determined by the transmission device a1, and is notified in advance from the transmission device a1 to the reception device b1.
The IFFT unit a105 performs frequency-time conversion on the frequency domain signal input from the mapping unit a104, and generates a time domain signal. Here, a time interval of a unit for performing IFFT is referred to as an FFT interval. The IFFT unit a105 outputs the generated time domain signal to the GI insertion unit a106.

The GI insertion unit a106 adds a guard interval for each signal in the FFT interval to the time domain signal input from the IFFT unit a105. Here, the guard interval is a duplicate of the rear part of the signal in the FFT interval, and the GI insertion unit a106 adds the duplicated signal to the front of the signal in the FFT interval.
The FFT interval and the time interval (referred to as GI interval) of the guard interval added to the signal in the time interval by the GI insertion unit a106 are collectively referred to as an OFDM symbol interval. A signal in the OFDM symbol section is called an OFDM symbol. The GI insertion unit a106 outputs a signal with the guard interval added to the transmission unit a107.
The transmission unit a107 performs digital / analog conversion on the signal input from the GI insertion unit a106, and shapes the waveform of the converted analog signal. The transmission unit a107 upconverts the waveform-shaped signal from the baseband to the radio frequency band, and transmits the signal from the transmission antenna a108 to the reception device b1.

<Configuration of Receiving Device b1>
FIG. 3 is a schematic block diagram illustrating the configuration of the receiving device b1 according to the present embodiment. In this figure, a receiving device b1 includes a receiving antenna b101, a receiving unit b102, a subtracting unit b103, a GI removing unit b104, an FFT unit b105, a propagation path estimating unit b106, a restoring unit b107, a demodulating unit b108, a decoding unit b109, a symbol replica. A generation unit b110, an IFFT unit b111, a GI insertion unit b112, and a filter unit b113 are included. Here, the subtraction unit b103, the GI removal unit b104, the FFT unit b105, the restoration unit b107, and the filter unit a113 are referred to as a signal extraction unit B1.

  The reception unit b102 receives the transmission signal transmitted from the transmission device a1 via the reception antenna b101. The receiving unit b102 performs frequency conversion and analog-digital conversion on the received signal. The receiving unit b102 stores the converted received signal. The reception unit b102 outputs the received signal to be stored to the subtraction unit b103 and the propagation path estimation unit b106 at the initial processing and the timing when the filter unit b113 described later inputs the reception signal replica to the subtraction unit b103.

The subtractor b103 subtracts the received signal replica input from the filter unit b113 described later from the received signal input from the receiver b102. The subtraction unit b103 outputs a signal obtained by subtracting the received signal replica to the GI removal unit b104.
In the case of the initial processing, there is no input from the filter unit b113 to the subtraction unit b103 (it is zero), and the subtraction unit b103 outputs the received signal input from the reception unit b102 to the GI removal unit b104 as it is.

The GI removal unit b104 removes the GI from the signal input from the subtraction unit b103, and outputs the signal from which the GI has been removed to the FFT unit b105.
The FFT unit b105 performs time-frequency conversion on the time domain signal input from the GI removal unit b104, and outputs the converted frequency domain signal to the restoration unit b107.

The propagation path estimation unit b106 estimates the channel impulse response in the OFDM symbol interval based on the reception signal input from the reception unit b102 and the transmission signal replica signal input from the GI insertion unit b112 described later. Here, for estimation of the channel impulse response, an RLS (Recursive Least Square) algorithm may be used, or other algorithms such as an LMS (Least Mean Square) algorithm may be used. Also good. In the case of the first processing, there is no input from the GI insertion unit b112 to the propagation path estimation unit b106 (it is zero), and the propagation path estimation unit b106 is input from the pilot signal stored in advance and the reception unit b102. Based on the received signal, a channel impulse response that varies in time in the OFDM symbol period is estimated.
The propagation path estimation unit b106 outputs the estimated channel impulse response to the filter unit b113. Moreover, the propagation path estimation part b106 performs time frequency conversion with respect to the estimated channel impulse response, and outputs the frequency response which is the signal of the converted frequency domain to the decompression | restoration part b107 and the demodulation part b108.

  Moreover, the propagation path estimation part b106 produces | generates the replica of a pilot signal from the estimated frequency response and the pilot signal stored beforehand. The propagation path estimation unit b106 calculates noise power based on the pilot signal of the received signal and the generated replica of the pilot signal. Further, the propagation path estimation unit b106 calculates ICI power (referred to as ICI power) based on the estimated frequency response and the pilot signal. Details of the noise power and ICI power calculation processing performed by the propagation path estimation unit b106 will be described later together with the operation principle. The propagation path estimation unit b106 outputs the calculated noise power and ICI power to the demodulation unit b108.

For each subcarrier, the restoration unit b107 multiplies a frequency response input from the propagation path estimation unit b106 by a symbol replica input from a symbol replica generation unit b110, which will be described later, to obtain a desired signal affected by the propagation path The replica signal is generated. The restoration unit b107 adds the generated replica signal to the signal input from the FFT unit b105 for each subcarrier. That is, the restoration unit b107 generates a replica signal of the desired signal based on the propagation path estimation value and the symbol replica, adds the replica signal of the desired signal to the frequency domain signal converted by the FFT unit b105, Each subcarrier component of the received signal is extracted.
The restoration unit b107 outputs a signal obtained by adding the replica signal to the demodulation unit b108.
In the first processing, there is no input from the symbol replica generation unit b110 to the restoration unit b107 (it is zero), and the restoration unit b107 outputs the signal input from the FFT unit b105 to the demodulation unit b108 as it is.
As described above, the signal extraction unit B1 removes the received signal replica from the received signal based on the propagation path estimation value and the symbol replica, and restores the desired signal to restore each of the received signals from which ICI (interference) is removed. Extract subcarrier components.

  The demodulation unit b108 calculates a filter coefficient using a ZF (Zero Forcing) standard, an MMSE (Minimum Mean Square Error) standard, and the like, using the frequency response, noise power, and ICI power input from the propagation path estimation unit b106. To do. The demodulator b108 compensates for fluctuations in the amplitude and phase of the signal (referred to as propagation path compensation) using the calculated filter coefficient. The demodulator b108 demaps the signal subjected to propagation path compensation based on the mapping information notified in advance from the transmission device a1, and performs demodulation processing on the demapped signal. The demodulator b108 outputs a bit log likelihood ratio (LLR) as a result of the demodulation process to the decoder b109.

The decoding unit b109 performs, for example, maximum likelihood decoding (MLD; Maximum Likelihood Decoding), maximum a posteriori probability estimation (MAP), log-MAP, Max on the demodulated symbols input from the demodulation unit b108. Decoding processing is performed using -log-MAP, SOVA (Soft Output Viterbi Algorithm), or the like.
When it is determined that no error is detected as a result of the decoding process, or when it is determined that a predetermined number of processes have been performed, the decoding unit b109 outputs the bit log likelihood ratio of the decoding result as information data bits. To do. On the other hand, when it is determined that an error has been detected and the prescribed number of processes have not been performed, the decoding unit b109 outputs the bit log likelihood ratio of the decoding result to the symbol replica generation unit b110.

  The symbol replica generation unit b110 calculates an expected value of the bit log likelihood ratio input from the decoding unit b109, decodes and modulates the calculated expected value, and generates a modulation symbol (referred to as a symbol replica). The symbol replica generation unit b110 maps the generated symbol replica based on the mapping information notified in advance from the transmission device a1. The symbol replica generation unit b110 outputs the mapped symbol replica to the restoration unit b107 and the IFFT unit b111.

The IFFT unit b111 performs frequency time conversion on the symbol replica input from the symbol replica generation unit b110, and outputs the converted time domain replica signal to the GI insertion unit b112.
The GI insertion unit b112 generates a transmission signal replica by adding a guard interval for each signal in the FFT interval to the replica signal input from the IFFT unit b111. The GI insertion unit b112 outputs the generated transmission signal replica to the propagation path estimation unit b106 and the filter unit b113.
The filter unit b113 generates a reception signal replica based on the channel impulse response input from the propagation path estimation unit b106 and the transmission signal replica input from the GI insertion unit b112. The filter unit b113 outputs the generated reception signal replica to the subtraction unit b103.
The reception device b1 repeatedly performs the processing from the subtraction unit b103 to the filter unit b113 on the same signal until the decoding unit b109 no longer detects an error or a predetermined number of times (referred to as repetition processing).

FIG. 4 is a schematic diagram illustrating an example of a received signal according to the present embodiment. This figure shows the case where the maximum delay does not exceed the GI length and there is no interference due to the previous OFDM symbol.
In this figure, received signals received via the propagation paths of propagation path numbers 1, 2, 3, and 4 in FIG. 1 are shown in order from the top as 0th path, 1st path, 2nd path, and 3rd path, respectively.
In FIG. 4, the horizontal axis is a time axis, which is discrete time divided by a predetermined time width. In this figure, a hatched area with a diagonally upward left diagonal line indicates a GI (Guard Interval). A hatched area with a diagonal line rising to the right indicates received signals of the preceding and succeeding OFDM symbols.
N is the number of points in the FFT (Fast Fourier Transform) section (also the number of points in the IFFT (Inverse Fast Fourier Transform) section), and N _g is the number of GI points. Here, the number of points is the number of discrete times.

<About the operating principle>
Hereinafter, the operating principle of the receiving device b1 will be described with reference to FIG.
First, the operation principle for the first process will be described. Received signal _{r k} of the k discrete time receiver b102 has received the following equation (1) is represented by (2).

Here, D is the maximum propagation path number, h _{d, k} is the complex amplitude at the k-th discrete time in the path of the propagation path number d (referred to as the d-th path), _sk is the time domain transmission signal, and z _k Is time domain noise. Further, N number of points of the FFT interval, _{S n} are the modulated signal of the first n subcarriers, _{N g} is the number of points the GI interval (see FIG. 4), j is the imaginary unit.
The reception signal _{r k} of the FFT interval (Figure 4 k = from _{N g k = N g + N} -1), at the FFT unit b105, the signal _{R n} after the time-frequency conversion, the following equation ( 3) and (4).

Here, W _{n, m} is a leakage coefficient of a signal from the m-th subcarrier to the n-th subcarrier, and Z _n is noise in the n-th subcarrier. In Equation (4), W _{n, n} when m = n is the frequency response of the n-th subcarrier, and is represented by the following Equation (5).

Note that equation (5) matches the discrete Fourier transform result for the time average of the channel impulse response that is time-varying within the OFDM symbol. In the initial processing, W _{n, n} is directly estimated using the propagation path estimation unit b106 and the pilot signal. In the initial processing, the signal represented by Expression (3) is output from the FFT unit b105 to the demodulation unit b108 as it is via the restoration unit b107. For example, when the MMSE standard filtering is used, the demodulator b108 calculates the demodulated symbol S ′ _n using the following equation (6).

Here, Y ^* indicates a complex conjugate of Y. In the initial process, since the reception process is performed without removing the ICI, the transmission characteristics deteriorate due to the influence. In Equation (6), σ _z ² is noise power, σ _I ² is ICI power, and the propagation path estimation unit b106 calculates using the following Equations (7) and (8).

Here, E [X] represents an ensemble average of X. In this embodiment, the propagation path estimation unit b106 uses the pilot signal to calculate the noise power σ _z ^{2 and the} ICI power σ _I ^{2, and} uses the result in equation (6) to demodulate the demodulated symbol S ′ _n. Is calculated.
Demodulator b108 calculates the bit log likelihood ratio from the demodulation symbol S _'n of formula (6). An equivalent amplitude gain is used for this calculation process. Specifically, in the case of QPSK, the bit log likelihood ratio λ is expressed by the following equations (10) and (11) with respect to the equivalent amplitude gain μ _n of the n-th subcarrier expressed by the following equation (9). Represented. Here, the equations (10) and (11) are respectively _{expressed by} bit log likelihood ratios λ (b _{n, 0} ) and λ (1) of the first bit b _{n, 0} and the second bit b _{n, 1.} b _{n, 1} ).

Next, the principle of operation for iterative processing will be described. The symbol replica generation unit b110 calculates an expected value of the bit log likelihood ratio decoded by the decoding unit b109, decodes and modulates the calculated expected value, and generates a symbol replica S ″ _n . The symbol replica S ″ _n is frequency-time converted by the IFFT unit b111, and the GI is inserted by the GI insertion unit b112. The transmission signal replica s ″ _k output from the GI insertion unit b112 is expressed by the following equation (12).

Here, in order to generate the transmission signal replica s ″ _k of Expression (12), the IFFT unit b111 performs inverse fast Fourier transform, and the order of the number of multiplications in this transform is O (Nlog ₂ N).
The propagation path estimation unit b106 estimates the channel impulse response hd _{, k} based on the transmission signal replica expressed by Expression (12) and the reception signal input from the reception unit b102. Further, the propagation path estimation unit b106 performs time-frequency conversion by averaging the channel impulse responses hd _{, k ,} and calculates the frequency response Wn _{, n} .
Based on the channel impulse response h _{d, k} and the transmission signal replica s ″ _k represented by the equation (12), the filter unit b113 converts the received signal replica r ″ _k represented by the following equation (13). Generate.

Note that the order of the number of multiplications in the processing performed by the filter unit b113 to generate the received signal replica of Expression (13) is O (DN). Here, since D << N in general, it may be considered as O (N).
The subtractor b103 subtracts the received signal replica r ″ _k represented by the equation (13) from the received signal r _k represented by the equation (1), and outputs a signal r ′ _k represented by the following equation (14). To do.

GI removal unit b104 removes the GI from the signal r _'k of the FFT interval, FFT section b105 is time-frequency converting a signal obtained by removing the GI. The signal R ′ _n output from the FFT unit b105 is expressed by the following equation (15).

Here, in order to generate the signal R ′ _n of Expression (15), the FFT unit b105 performs a fast Fourier transform, and the order of the number of multiplications in this transform is O (Nlog ₂ N).
The restoration unit b107 multiplies the symbol replica S ″ _n by the frequency response W _{n, n} to generate a replica signal W _{n, n} S ″ _n of the desired signal affected by the propagation path. The restoration unit b107 adds the generated replica signal W _{n, n} S ″ _n to the signal R ′ _n represented by Expression (15). The signal Y _n after the addition is expressed by the following equation (16).

This equation (16) means that the desired signal of the nth subcarrier remains and the ICI is removed. By removing ICI, the signal-to-interference noise power ratio (SINR) can be improved, and the transmission characteristics are improved.
Also, restoration section b107 is for performing processing for generating a signal Y _n of the formula (16) for each subcarrier, the order of the number of multiplications in this process is O (N). Demodulator b108, for example when using a filtering MMSE criterion, demodulate by calculating a demodulated symbol S _'n of the n sub-carrier represented by the following formula from the signal _{Y n} of the formula (16) (17) .

In the present embodiment, the restoration unit b107 calculates a demodulated symbol S ′ _n using an approximate expression (19) described later.
The decoding unit b109 performs a decoding process on the bit log likelihood ratios λ (b _{n, 0} ) and λ (b _{n, 1} ) of the demodulated symbol S ′ _n expressed by Expression (17). Thereafter, the iterative process is repeated. By repeating the above-described iterative process, the transmission characteristics can be greatly improved.
In addition, in the frequency response W _{n, n} represented by the equation (5), the center value of the symbol of the changing channel impulse response may be used instead of the channel impulse response in the equation (5). In this case, the frequency response W _{n, n} used instead of the equation (5) is expressed by the following equation (18).

Thereby, the calculation process of frequency response Wn _{, n} can be reduced.
Equation (17) also takes into account that the removal residual due to the received signal replica is accurately taken into account, prior information is obtained by decoding processing, and that the power of the modulation symbol of each subcarrier cannot be normalized to 1. This is the formula when On the other hand, the removal residual may be approximated with noise, and the power of the demodulated symbol may be normalized to 1. In this case, the demodulator b108 calculates the demodulated symbol S ′ _n using the following equation (19).

Here, σ _{I ′} ² is the power of the ICI removal residual (ensemble average for the subcarriers of the signal R ′ _n ). Even if it does in this way, a characteristic does not deteriorate. In Expression (17), the number of multiplications of order O (N ² ) is necessary for calculating the ICI removal residual term of the second term of the denominator. However, by using Expression (19), processing can be performed with the number of multiplications of order O (N), and the number of multiplications can be greatly reduced. Therefore, the order of the maximum number of multiplications in each part of the iterative process is O (Nlog ₂ N), and the receiving apparatus b1 can perform the iterative process by the process of the number of multiplications of order O (Nlog ₂ N).

<Operation of Receiving Device b1>
FIG. 5 is a flowchart showing the operation of the receiving device b1 according to this embodiment. The operation shown in this figure is processing after the reception unit b102 in FIG. 3 outputs the reception signal to the subtraction unit b103 for the first time.

(Step S101) The subtraction unit b103 subtracts the reception signal replica generated in step S108 described later from the reception signal. Then, it progresses to step S102.
(Step S102) The FFT unit b105 performs time-frequency conversion on the signal resulting from the subtraction in Step S101. Thereafter, the process proceeds to step S103.
(Step S103) The restoration unit b107 adds, for each subcarrier, a replica signal obtained by multiplying a symbol replica generated in step S107 described later by a frequency response to the signal of the conversion result in step S102. Thereafter, the process proceeds to step S104.

(Step S104) The demodulation unit b108 performs propagation path compensation on the signal resulting from the addition in step S103, and calculates a bit log likelihood ratio. Thereafter, the process proceeds to step S105.
(Step S105) The decoding unit b109 performs decoding processing such as error correction on the bit log likelihood ratio of the calculation result in step S104. Thereafter, the process proceeds to step S106.
(Step S106) The decoding unit b109 determines whether an error is not detected in the decoding result in step S105, or whether a predetermined number of processes have been performed. If any of these is true (Yes), the receiving apparatus b1 ends the operation. On the other hand, when it does not correspond to both of these (No), it progresses to step S107. Note that the determination of whether or not there is an error in the decoding result may be performed, for example, in a MAC (Media Access Control) layer.

(Step S107) The symbol replica generation unit b110 generates a symbol replica from the bit log likelihood ratio of the decoding result in step S105. Thereafter, the process proceeds to step S108.
(Step S108) The IFFT unit b111, the GI insertion unit b112, and the filter unit b113 generate a received signal replica based on the symbol replica generated in step S107. Then, it progresses to step S101.

  Thus, according to the present embodiment, the receiving apparatus b1 extracts each subcarrier component of the received signal from which ICI is removed, and demodulates the signal of each extracted subcarrier component. Thereby, the receiving device b1 can prevent an increase in the calculation amount.

<Experimental result>
Hereinafter, the result of the computer simulation performed to show the effectiveness of the communication system according to the present embodiment will be described.
FIG. 6 is a schematic diagram illustrating an example of simulation conditions of the communication system according to the present embodiment. In the simulation of this example, the simulation was performed under the conditions of FIG.

  FIG. 7 is a schematic diagram illustrating an example of a simulation result of the communication system according to the present embodiment. In this figure, the horizontal axis represents average Es / No (average reception energy to noise power density ratio), and the vertical axis represents average frame error rate (FER) characteristics. This figure shows the result of the simulation performed under the simulation conditions of FIG.

  In FIG. 7, a graph denoted by reference sign P1 indicates a characteristic (referred to as characteristic 1) when only the initial process is performed (no repetition process is performed). Further, the graph denoted by reference symbol P2 indicates a characteristic (referred to as characteristic 2) in the receiving apparatus b1 according to the present embodiment. Further, the graph denoted by reference symbol P3 shows a characteristic (referred to as characteristic 3) when only the initial process is performed when there is no propagation path variation (the maximum Doppler frequency is 0 Hz). Comparing characteristic 1 and characteristic 2, it is possible to remove ICI due to high-speed movement (large propagation path fluctuation), so when the average Es / No is 16 dB, the average FER is 0.6 in the former The latter is 0.006, which shows that the accuracy is greatly improved. Further, it can be seen that the characteristic 2 is more accurate than the characteristic 3. This is because the time diversity effect can be obtained by changing the propagation path.

In the first embodiment, the filter unit b113 generates a reception signal replica, the subtraction unit b103 subtracts the reception signal replica, and the restoration unit b107 adds the replica signal of the desired signal. The case where demodulation processing is performed has been described. However, the present invention is not limited to this, the filter unit b113 generates a signal replica obtained by removing the received signal of the desired signal from the received signal, and the subtracting unit b103 subtracts the signal replica and performs demodulation processing for each subcarrier. May be.
In this case, the above equation (14) is replaced by the following equations (20) and (21).

  In the first embodiment described above, the communication system performs communication of multicarrier signals. However, the present invention is not limited to this, and is also applicable to communication of single carrier signals using FFT. can do.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described in detail with reference to the drawings. In the present embodiment, a case will be described in which the receiving apparatus demodulates a received signal using a signal leaked from a desired subcarrier to another subcarrier due to propagation path fluctuation.
Since the conceptual diagram of the communication system according to the present embodiment is the same as that of the first embodiment (FIG. 1), description thereof is omitted. Here, the transmission apparatus A according to the present embodiment is the same transmission apparatus a1 as that of the first embodiment, and thus description thereof is omitted. Hereinafter, in the present embodiment, the receiving device B is referred to as a receiving device b2.

  FIG. 8 is a schematic block diagram showing the configuration of the receiving device b2 according to the second embodiment of the present invention. When the receiving apparatus b2 (FIG. 8) according to the present embodiment is compared with the receiving apparatus b1 (FIG. 3) according to the first embodiment, an FFT unit b205, a propagation path estimating unit b206, a restoring unit b207, and a demodulating unit b208. Is different. However, other components (reception antenna b101, reception unit b102, subtraction unit b103, GI removal unit b104, decoding unit b109, symbol replica generation unit b110, IFFT unit b111, GI insertion unit b112, and filter unit a113) are included. The function is the same as in the first embodiment. A description of the same functions as those in the first embodiment is omitted. Note that the subtraction unit b103, the GI removal unit b104, the FFT unit b205, the restoration unit b207, and the filter unit a113 are referred to as a signal extraction unit B2.

  The FFT unit b205 performs time-frequency conversion on the time-domain signal input from the GI removal unit b104, and outputs the converted frequency-domain signal to the restoration unit b207. Here, the FFT unit b205 is a peripheral n + 1 subcarrier (l = 1, −1, 2, −2,..., L, −L) with respect to the nth subcarrier signal of the restoration unit b207. Are output together. The subcarrier number n is a number assigned in ascending order from the highest frequency to the lowest frequency.

  In addition to the process of the propagation path estimation unit b106 according to the first embodiment, the propagation path estimation unit b206 calculates a leak coefficient from the nth subcarrier to the n + 1th subcarrier based on the pilot signal. The propagation path estimation unit b206 outputs the calculated leakage coefficient to the restoration unit b207 and the demodulation unit b208.

The reconstruction unit b207 multiplies the leakage coefficient input from the propagation path estimation unit b206 by the symbol replica input from the symbol replica generation unit b110 for each subcarrier to change from the nth subcarrier to the n + 1 subcarrier. A replica signal (referred to as an (n + 1) th leaky replica signal) of the leaked desired signal is generated. The restoration unit b207 adds the generated n + 1 leaky replica signal to the n + 1 subcarrier signal input from the FFT unit b205. That is, the restoration unit b207 extracts the subcarrier component of the frequency domain signal converted by the FFT unit b205, and the subcarrier component of the replica signal of the desired signal is extracted from the extracted subcarrier component signal. The subcarrier components close to the carrier are added.
The restoration unit b207 outputs a signal obtained by adding the (n + 1) th leakage replica signal to the demodulation unit b208.

  The demodulator b208 uses the leakage coefficient, noise power, and ICI power input from the propagation path estimation unit b206 to calculate filter coefficients using a ZF (Zero Forcing) standard, an MMSE standard, and the like. The demodulator b208 performs propagation path compensation using the calculated filter coefficient. The demodulator b208 demaps the signal subjected to propagation path compensation based on the mapping information notified in advance from the transmission device a1, and performs demodulation processing on the demapped signal. The demodulation unit b208 outputs the bit log likelihood ratio as a result of the demodulation process to the decoding unit b109.

<About the operating principle>
Hereinafter, the operating principle of the receiving device b2 will be described with reference to FIG. First, the operation principle for the first process is the same as that in the first embodiment, and a description thereof will be omitted. Hereinafter, the operation principle of the iterative process will be described.

As described in the first embodiment, the signal R _'n of the n sub-carriers FFT unit b205 outputs are represented by the formula (15). Therefore, the signal R ′ _{n + 1} of the ( _{n + 1} ) _th subcarrier is expressed by the following equation (22).

Equation (22) modified as described above indicates that the first term is an element of the nth subcarrier. The restoration unit b207 multiplies the symbol replica S ″ _n by the frequency response W _{n + 1, n} to generate the ( _{n + 1) th} leaky replica signal W _{n + 1, n} S ″ _n . Restoring unit b207 is' generated on the _{n + l,} the n + l leak-replica signal _{W n + l, n} S 'signal R of formula (22) adds _{a' n.} The signal X _{n, l} after this addition is expressed by the following equation (23).

The demodulator b108 calculates the demodulated symbol S ′ _n of the n-th subcarrier using the following equation (24). However, the following expression (24) is an expression when the removal residual is approximated with noise and the power of the demodulated symbol is normalized to 1.

  In each subcarrier, the power of the signal leaking from other subcarriers decreases as the frequency difference increases. Therefore, in the receiving device b1, L may be determined in advance, for example, L = ± 1. That is, it may be a value considering only two adjacent subcarriers. Further, as described above, the receiving apparatus b1 uses information on the large and small L subcarriers for the frequency from the nth subcarrier for processing. However, the present invention is not limited to this, and processing may be performed using a different number of subcarriers in the frequency magnitude direction, or processing may be performed using only either the frequency major direction or the minor direction. You may go.

<Operation of Receiving Device b2>
FIG. 9 is a flowchart showing the operation of the receiving device b2 according to this embodiment. The operation shown in this figure is processing after the reception unit b102 in FIG. 8 outputs the reception signal to the subtraction unit b103 for the first time.
When the operation of the receiving device b2 according to the present embodiment (FIG. 9) and the operation of the receiving device b1 according to the first embodiment (FIG. 5) are compared, the processes in steps S203 and S204 are different. However, other processes (steps S101, S102, and S105 to S108) are the same as those in the first embodiment. A description of the same processing as in the first embodiment is omitted.

(Step S203) For each subcarrier, the restoration unit b207 obtains the (n + 1) th leakage replica obtained by multiplying the symbol replica generated in step S107 by the leakage coefficient with respect to the signal of the (n + 1) th subcarrier converted in step S102. Add the signals. Thereafter, the process proceeds to step S204.
(Step S204) The demodulator b207 performs channel compensation on the signal resulting from the addition in step S203, and calculates a bit log likelihood ratio. Thereafter, the process proceeds to step S105.

  Thus, according to the present embodiment, the receiving apparatus b2 adds the subcarrier component of the replica signal of the desired signal and the subcarrier component close to the subcarrier to the subcarrier component signal. . As a result, the receiving apparatus b2 can improve SINR and obtain high transmission characteristics.

(Third embodiment)
Hereinafter, the third embodiment of the present invention will be described in detail with reference to the drawings. In the present embodiment, a case will be described in which the communication system performs communication using a MIMO (Multiple Input Multiple Output) transmission method.
Since the conceptual diagram of the communication system according to the present embodiment is the same as that of the first embodiment (FIG. 1), description thereof is omitted. Hereinafter, in the present embodiment, the transmission device A is referred to as a transmission device a3, and the reception device B is referred to as a reception device b3. In the present embodiment, a case will be described in which a receiving device b3 having R antennas receives a signal transmitted by a transmitting device a3 having T antennas. Here, the receiving apparatus b3 receives T streams transmitted from the transmitting apparatus a3 through the T antennas through the R antennas, and performs MIMO separation.

<About the configuration of the transmission device a3>
FIG. 10 is a schematic block diagram showing the configuration of the transmission device a3 according to the third embodiment of the present invention. In this figure, a transmission device a3 includes a pilot generation unit a301-t (t = 1, 2,... T, the same shall apply hereinafter), a coding unit a302-t, a modulation unit a303-t, a mapping unit a304-t, and an IFFT. Unit 305-t, GI insertion unit a306-t, transmission unit a307-t, and transmission antenna unit a308-t.

The pilot generation unit a301-t generates a pilot signal in which the receiving device b3 stores in advance the amplitude value of the waveform (or the signal sequence), and outputs the pilot signal to the mapping unit a304-t.
The encoding unit a302-t encodes information bits to be transmitted to the reception device b3 using an error correction code such as a convolutional code, a turbo code, and an LDPC code, and generates encoded bits. The encoding unit a302-t outputs the generated encoded bits to the modulation unit a303-t.
The modulation unit a303-t modulates the coded bits input from the coding unit a302-t using a modulation scheme such as PSK or QAM, and generates a modulation symbol. The modulation unit a303-t outputs the generated modulation symbol to the mapping unit a304-t.

The mapping unit a304-t maps the pilot signal input from the pilot generation unit a301-t and the modulation symbol input from the modulation unit a303-t to resources based on predetermined mapping information, and performs frequency domain And the generated frequency domain signal is output to the IFFT unit a305-t. Also, the mapping information is determined by the transmission device a3 and is notified in advance from the transmission device a3 to the reception device b3.
The IFFT unit a305-t performs frequency-time conversion on the frequency domain signal input from the mapping unit a304-t to generate a time domain signal. The IFFT unit a305-t outputs the generated time domain signal to the GI insertion unit a306-t.

The GI insertion unit a306-t adds a guard interval for each signal in the FFT interval to the time domain signal input from the IFFT unit a305-t. Here, the guard interval is a duplicate of the rear part of the signal in the FFT interval, and the GI insertion unit a306-t adds the duplicated signal to the front of the signal in the FFT interval.
The GI insertion unit a306-t outputs a signal with the guard interval added to the transmission unit a307-t.
The transmission unit a307-t performs digital / analog conversion on the signal input from the GI insertion unit a306-t, and shapes the converted analog signal. The transmission unit a307-t upconverts the waveform-shaped signal from the baseband to the radio frequency band, and transmits the signal from the transmission antenna a308-t to the reception device b3.

<About the configuration of the receiving device b3>
FIG. 11 is a schematic block diagram showing the configuration of the receiving device b3 according to this embodiment. In this figure, the receiving device b3 includes a receiving antenna b301-r (r = 1, 2,... R, the same applies hereinafter), a receiving unit b302-r, a subtracting unit b303-r, a GI removing unit b304-r, and an FFT. Unit b305-r, reception signal replica generation unit B3-r, restoration unit b307-r, demodulation unit b308, decoding unit b309-t, and symbol replica generation unit b310-t. Note that the subtraction units b303-1 to b303-R, the GI removal units b304-1 to b304-R, the FFT units b305-1 to b305-R, the restoration units b307-1 to b307-R, and the received signal replica generation unit B3- 1 to B3-R (filter units b313-1 to b313-R described later) are referred to as a signal extraction unit B3.

  The reception unit b302-r receives the transmission signal transmitted from the transmission device a3 via the reception antenna b301-r. The receiving unit b302-r performs frequency conversion and analog-digital conversion on the received signal. The receiving unit b302-r stores the converted received signal. The reception unit b302-r generates the reception signal to be stored and the subtraction unit b303-r and the reception signal replica generation at the initial process and the timing when the filter unit b313-r described later inputs the reception signal replica to the subtraction unit b303-r. Output to part B3-r.

The subtraction unit b303-r subtracts the reception signal replica input from the reception signal replica generation unit B3-r described later from the reception signal input from the reception unit b302-r. The subtraction unit b303-r outputs a signal obtained by subtracting the received signal replica to the GI removal unit b304-r.
In the case of the initial processing, there is no input from the reception signal replica generation unit B3-r to the subtraction unit b303-r (it is zero), and the subtraction unit b303-r receives the reception signal input from the reception unit b302-r. Is directly output to the GI removal unit b304-r.

The GI removal unit b304-r removes the GI from the signal input from the subtraction unit b303-r and outputs the signal from which the GI has been removed to the FFT unit b305-r.
The FFT unit b305-r performs time-frequency conversion on the time domain signal input from the GI removal unit b304-r, and outputs the converted frequency domain signal to the restoration unit b307-r.

The reception signal replica generation unit B3-r estimates the frequency response from each of the antennas a308-t (referred to as the t-th antenna) of the transmission device a3 to the antenna b301-r (referred to as the r-th antenna), and the restoration unit b307-r and It outputs to the demodulation part b308. Also, the reception signal replica generation unit B3-r calculates noise power and ICI power, and outputs them to the demodulation unit b308.
The reception signal replica generation unit B3-r generates a reception signal replica of the reception signal received by the r-th antenna from the symbol replica input from the symbol replica generation unit b310-t, and outputs the reception signal replica to the subtraction unit b303-r. To do. Details of the configuration and processing of the reception signal replica generation unit B3-r will be described later.

For each subcarrier, the restoration unit b307-r multiplies the frequency response input from the propagation path estimation unit b306 by a symbol replica input from a symbol replica generation unit b310-t described later, to thereby influence the propagation path. A replica signal of the received desired signal is generated. The restoration unit b307-r adds the generated replica signal to the signal input from the FFT unit b305-r for each subcarrier. That is, the restoration unit b307-r extracts the subcarrier component of the frequency domain signal transformed by the FFT unit b305-r, and the subcarrier component of the replica signal of the desired signal is extracted from the extracted subcarrier component signal. Among these, a desired stream (t-th stream) component is added. The restoration unit b307-r outputs a signal obtained by adding the replica signal to the demodulation unit b308.
In the case of the first processing, there is no input from the symbol replica generation unit b310-t to the restoration unit b307-r (zero), and the symbol replica generation unit b310-t is input from the FFT unit b305-r. The signal is output as it is to the demodulator b308.

  The demodulation unit b308 calculates filter coefficients using the ZF criterion, the MMSE criterion, and the like using the frequency response, noise power, and ICI power input from the propagation path estimation unit b306-r. The demodulator b308 performs propagation path compensation using the calculated filter coefficient. The demodulator b308 demaps the signal subjected to propagation path compensation based on the mapping information notified in advance from the transmission device a3, and performs demodulation processing on the demapped signal. The demodulation unit b309-t outputs a bit log likelihood ratio as a result of the demodulation processing to the decoding unit b309-t for the signal of the transmission signal sequence (referred to as the tth stream) transmitted from the tth antenna.

The decoding unit b309-t performs a decoding process on the demodulated symbol input from the demodulation unit b308 using, for example, maximum likelihood decoding, maximum posterior probability estimation, log-MAP, Max-log-MAP, SOVA, and the like. I do.
When it is determined that no error is detected as a result of the decoding process, or when it is determined that a predetermined number of processes have been performed, the decoding unit b309-t sets the bit log likelihood ratio of the decoding result as an information data bit. Output as. On the other hand, when it is determined that an error has been detected and the specified number of processes has not been performed, the decoding unit b309-t sends the bit log likelihood ratio of the decoding result to the symbol replica generation unit b310-t. Output.

  The symbol replica generation unit b310-t calculates an expected value of the bit log likelihood ratio input from the decoding unit b309-t, decodes and modulates the calculated expected value, and generates a symbol replica. The symbol replica generation unit b310-t maps the generated symbol replica based on mapping information notified in advance from the transmission device a3. The symbol replica generation unit b310 outputs the mapped symbol replicas to the restoration units b307-1 to b307-R and the reception signal replica generation units B3-1 to B3-R.

  FIG. 12 is a schematic block diagram illustrating a configuration of the reception signal replica generation unit B3-r according to the present embodiment. In this figure, the received signal replica generation unit B3-r includes an IFFT unit b311-t, a GI insertion unit b312-t, a propagation path estimation unit b306, a filter unit b313-t, and a summation unit b314. .

The IFFT unit b311-t performs frequency time conversion on the symbol replica input from the symbol replica generation unit b310-t, and outputs the converted time domain replica signal to the GI insertion unit b312-t.
The GI insertion unit b312-t adds a guard interval for each signal in the FFT interval to the replica signal input from the IFFT unit b311-t to generate a transmission signal replica. The GI insertion unit b312-t outputs the generated transmission signal replica to the propagation path estimation unit b306 and the filter unit b313-t.

Based on the received signal input from the receiving unit b302-r and the transmission signal replica signal input from the GI inserting unit b312-t, the propagation path estimation unit b306 receives the signal from each of the t-th antennas in the OFDM symbol period. Estimate the channel impulse response of the propagation path to the r antenna. In the case of the first processing, there is no input from the GI insertion unit b312-t to the propagation path estimation unit b306 (zero), and the propagation path estimation unit b306 stores the pilot signal stored in advance and the reception unit b302-r. Based on the received signal input from, a channel impulse response that varies with time in the OFDM symbol period is estimated.
The propagation path estimation unit b306 outputs the estimated channel impulse response to the filter unit b313-t. Moreover, the propagation path estimation part b306 performs time frequency conversion with respect to the estimated channel impulse response, and outputs the frequency response which is the signal of the converted frequency domain to the decompression | restoration part b307-r and the demodulation part b308.

  Moreover, the propagation path estimation part b306 produces | generates the replica of a pilot signal from the estimated frequency response and the pilot signal memorize | stored previously. The propagation path estimation unit b306 calculates noise power based on the pilot signal of the received signal and the generated replica of the pilot signal. Also, the propagation path estimation unit b306 calculates ICI power (referred to as ICI power) based on the estimated frequency response and pilot signal. Details of the noise power and ICI power calculation processing performed by the propagation path estimation unit b306 will be described later together with the operation principle. The propagation path estimation unit b306 outputs the calculated noise power and ICI power to the demodulation unit b308.

Based on the channel impulse response input from the propagation path estimation unit b306 and the transmission signal replica input from the GI insertion unit b312-t, the filter unit b313-t transmits the t-th stream received by the r-th antenna. A received signal replica is generated. The filter unit b313-t outputs the generated reception signal replica to the synthesis unit b314.
The combiner b314 combines the received signal replicas input from the filter unit b313-t, and generates a received signal replica of the received signal received by the r-th antenna. The synthesizer b314 outputs the generated received signal replica to the subtractor b303-r.

<About the operating principle>
Hereinafter, the operating principle of the receiving device b3 will be described with reference to FIGS. The received signals rk _{, r at} the k-th discrete time received by the receiving unit b302-r are _expressed by the following equations (25) and (26).

Here, T is the number of antennas of the transmitting device a3, D is the maximum propagation path number, _{hd, k, r, and t} are complex amplitudes at the k-th discrete time in the d-th path from the t-th antenna to the r-th antenna. It is. Further, s _{k, t} is a time domain transmission signal of the t th stream, and z _{k, r} is time domain noise at the r th antenna.
N is the number of points in the FFT interval, S _{n, t} is the modulation signal of the n-th subcarrier of the t-th stream, N _g is the number of points in the GI interval, and j is an imaginary unit.

The subtraction unit b303-r subtracts the received signal replica from the signal rk _{, r} expressed by the equation (25). The GI removal unit b304-r removes the GI from the signal in the FFT interval as the subtraction result, and the FFT unit b305-r performs time-frequency conversion on the signal from which the GI has been removed. The signal R ′ _{n, r} output from the FFT unit b305-r is _expressed by the following equations (27) and (28).

Here, W _{n, m, r, t} are leakage coefficients of signals from the m-th subcarrier to the n-th subcarrier for the t-th stream received by the r-th antenna, and leakage when m = n. The coefficients W _{n, n, r, t} are frequency responses. S ″ _{m, t} is a symbol replica of the signal of the nth subcarrier of the tth stream.
The restoration unit b307-r multiplies the symbol replica S ″ _{n, t} by the frequency response W _{n, n, r, t} input from the propagation path estimation unit b306, and is affected by the propagation path to receive the r-th antenna. Generates a replica signal W _{n, n, r, t} S ″ _{n, t} of a desired signal for the n-th subcarrier of the t-th stream received. The restoration unit b307-r adds the generated replica signal W _{n, n, r, t} S ″ _{m, t} to the signal R ′ _{n, r} represented by Expression (27). That is, the restoration unit b307-r extracts the subcarrier component of the frequency domain signal transformed by the FFT unit b305-r, and the subcarrier component of the replica signal of the desired signal is extracted from the extracted subcarrier component signal. The desired stream component is added. The signal Y _{n, r, t} after this addition is expressed by the following equation (29).

Here, since the third term of Expression (29) indicates that signals of other streams have been removed, Expression (29) means that MIMO separation has been performed.
The demodulation unit b308 calculates the demodulation symbol S ′ _{n, t} of the nth subcarrier of the tth stream using the following equation (30). However, the following equation (30) is an equation when the removal residual is approximated with noise and the power of the demodulated symbol is normalized to 1.

<About the operation of the receiving device b3>
FIG. 13 is a flowchart showing the operation of the receiving device b3 according to this embodiment. The operation shown in FIG. 11 is processing after the reception unit b302-r in FIG. 11 outputs the reception signal to the subtraction unit b303-r for the first time.

(Step S301) The subtraction unit b303-r subtracts the reception signal replica input from step S308 described later from the reception signal. Thereafter, the process proceeds to step S302.
(Step S302) The FFT unit b305 performs time-frequency conversion on the signal resulting from the subtraction in step S301. Thereafter, the process proceeds to step S303.
(Step S303) For each subcarrier, the restoration unit b307-r adds a replica signal obtained by multiplying a symbol replica generated in step S307, which will be described later, by a frequency response to the signal resulting from the conversion in step S302. Thereafter, the process proceeds to step S304.

(Step S304) The demodulator b308 performs propagation path compensation on the signal resulting from the addition in step S303, and calculates a bit log likelihood ratio. Thereafter, the process proceeds to step S305.
(Step S305) The decoding unit b309-t performs decoding processing such as error correction on the bit log likelihood ratio of the calculation result in step S304. Thereafter, the process proceeds to step S306. .
(Step S306) The decoding unit b309-t determines whether no error is detected in the decoding result in step S305 or whether a predetermined number of processes have been performed. If any of these is true (Yes), the receiving device b3 ends the operation. On the other hand, when it does not correspond to both of these (No), it progresses to step S307.

(Step S307) The symbol replica generation unit b310-t generates a symbol replica from the bit log likelihood ratio of the decoding result in step S305. Thereafter, the process proceeds to step S308.
(Step S308) The reception signal replica generation unit B3-r generates a reception signal replica based on the symbol replica generated in step S307. Then, it progresses to step S301.

  Thus, according to the present embodiment, the receiving device b3 extracts each subcarrier component of the received signal from which the delayed wave is removed, and demodulates the extracted signal of each subcarrier component. Thereby, the receiving apparatus b3 can prevent an increase in the amount of calculation even in the case of the MIMO transmission method.

In the third embodiment, the receiving device b3 does not restore signals of other streams even if it is a desired subcarrier, but may restore it. That is, you may restore | restore the 3rd term of Formula (29). In this case, the demodulator performs MIMO separation, and not only linear processing such as ZF and MMSE, but also maximum likelihood detection (MLD; Maximum Likelihood Detection; hereinafter, the abbreviation MLD means maximum likelihood detection) It is also possible to perform nonlinear processing such as
Hereinafter, the principle of the bit log likelihood ratio calculation process performed by the receiving apparatus b3 using the MLD when signals of other streams are also restored will be described.

The restoration unit b307-r adds the generated replica signals W _{n, n, r, t} S ″ _{m, t} to the signal R ′ _{n, r} represented by the equation (27) for all t. That is, the restoration unit b307-r extracts the subcarrier component of the frequency domain signal transformed by the FFT unit b305-r, and the subcarrier component of the replica signal of the desired signal is extracted from the extracted subcarrier component signal. All stream components are added. The signal Y _{n, r, t} after this addition is expressed by the following equations (31) and (32).

  When these equations (31) and (32) are expressed as vectors, they are represented by the following equations (33) to (36).

Here, the following equation bit sequence β constituting the vector _{S n} of the formula (35) (37).

However, M is a modulation multi-level number. For example, M = 2 in QPSK, and M = 4 in 16QAM. The bit log likelihood ratio λ (b _{t, q} ) of the bits b _{t, q} in Expression (37) is expressed by the following Expression (38).

Here, using Bayes' theorem, p (A | B) p (B) = p (B | A) p (A), the bit log likelihood ratio λ (b _{t, q} ) in equation (38) is Is represented by the following equation (39).

Further, assuming that Z ′ _{n, r} follows a Gaussian process and using the Max-log approximation, the bit log likelihood ratio λ (b _{t, q} ) of Expression (39) is expressed by the following Expression (40). .

  Assuming that each bit is independent, p (β) in Expression (40) is expressed by Expression (41) below.

Here, p (b _{t ′, q ′} ) can be calculated using the bit log likelihood ratio λ _a (b _{t ′, q ′} ) output from the decoding unit b309-t ′. Further, since the bit log likelihood ratio λ (b _{t, q} ) obtained in this way is calculated using the bit log likelihood ratio λ _a (b _{t, q} ), the corresponding amount is subtracted. It is common. That is, the value output from the demodulation unit b308 to the decoding unit b309-t is λ (b _{t, q} ) −λ _a (b _{t, q} ).
For simplicity, the LLR may be calculated on the assumption that there is no prior information. In this case, the bit log likelihood ratio λ (b _{t, q} ) is expressed by the following equation (42).

The demodulator b308 calculates the bit log likelihood ratio λ (b _{t, q} ) as a result of the demodulation process using the equation (42), and outputs it to the decoder b109-t.

In the third embodiment, similarly to the second embodiment, a received signal may be demodulated using a signal leaked from a desired subcarrier to another subcarrier.
In the third embodiment, the transmission device a3 (FIG. 10) includes one encoding unit a302-t for one antenna a308-t. However, the present invention is not limited to this. Instead, one encoding unit may be provided for a plurality of antennas. For example, the transmission device b3 may include one encoding unit, and distribute and output the result of error correction encoding to the modulation units a303-1 to a303-T according to a predetermined pattern.
In the third embodiment, the first to T-th streams may include transmission signals of the same information data signal sequence, or may be transmission signals of different information data signal sequences. For example, when transmitting two information data signal sequences, the transmission device a3 may transmit one information data sequence as the first and second streams and transmit the other information data signal sequence as the third and fourth streams. Good.

  Note that some of the receiving devices b1, b2, and b3 in the above-described embodiment, for example, the receiving units b102 and b302-r, the subtracting units b103 and b303-r, the GI removing units b104 and b304-r, and the FFT units b105 and b205. , B305-r, propagation path estimation units b106, b206, b306, restoration units b107, b207, b307-r, demodulation units b108, b208, b308, decoding units b109, b309-t, symbol replica generation units b110, b310-t The IFFT units b111 and b311-t, the GI insertion units b112 and b312-t, the filter units a113 and b313-t, and the synthesis unit b314 may be realized by a computer. In that case, the program for realizing the control function may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read by a computer system and executed. Here, the “computer system” is a computer system built in the receiving devices b1, b2, and b3 and includes hardware such as an OS and peripheral devices. The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, the “computer-readable recording medium” is a medium that dynamically holds a program for a short time, such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line, In such a case, a volatile memory inside a computer system serving as a server or a client may be included and a program that holds a program for a certain period of time. The program may be a program for realizing a part of the functions described above, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system.

  As described above, the embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the scope of the present invention. It is possible to

  The present invention is suitable for use in receiving wireless communication.

  A, a1, a3 ... transmitting device, B, b1, b2, b3 ... receiving device, a101, a301-t ... pilot generating unit, a102, a302-t ... coding unit, a103, a303 -T: modulation unit, a104, a304-t ... mapping unit, a105, a305-t ... IFFT unit, a106, a306-t ... GI insertion unit, a107, a307-t ... Transmitting unit, a108, a308-t ... transmitting antenna unit, b101, b301-r ... receiving antenna, b102, b302-r ... receiving unit, b103, b303-r ... subtracting unit, b104, b304-r ... GI removal unit, b105, b205, b305-r ... FFT unit, b106, b206, b306 ... propagation path estimation unit, b107, b207, b307- ... Restoration part, b108, b208, b308 ... Demodulation part, b109, b309-t ... Decoding part, b110, b310-t ... Symbol replica generation part, b111, b311-t ... IFFT , B112, b312-t ... GI insertion unit, a113, b313-t ... filter unit, B3-r ... received signal replica generation unit, b314 ... synthesis unit

Claims (12)

In a receiving device that demodulates information from a received signal,
A channel impulse response at a plurality of times in an OFDM symbol interval is estimated, the estimated channel impulse response at a plurality of times is converted into a single channel impulse response, and a time-frequency conversion is performed on the converted channel impulse response. A channel estimator for estimating the frequency response;
A symbol replica generation unit that generates a symbol replica that is a modulation symbol of the demodulated information;
A filter unit that generates a received signal replica that is a received signal replica in the time domain based on the channel impulse response of the plurality of times and the symbol replica;
A subtractor for subtracting the received signal replica from the received signal;
A time-frequency converter that converts the signal subtracted by the subtractor into a signal in the frequency domain;
A replica signal of a desired signal is generated based on the frequency response and the symbol replica, the replica signal of the desired signal is added to the frequency domain signal converted by the time-frequency conversion unit, and each received signal A restoration unit for extracting subcarrier components;
A demodulator that demodulates the signal of each subcarrier component extracted by the restoration unit;
A receiving apparatus comprising: The propagation path estimator is
Estimating the frequency response by performing time-frequency conversion on the time-averaged result of time averaging the channel impulse responses of the plurality of times;
The receiving apparatus according to claim 1. The propagation path estimator is
The plurality of times of the impulse response of the channel, the reception of claim 1, wherein the estimating the frequency response by performing a time-frequency transform on the channel impulse response of one time in the OFDM symbol interval apparatus. The receiving apparatus according to claim 3, wherein the channel impulse response at the one time is in the center of the OFDM symbol period. The restoration unit extracts a subcarrier component of the frequency domain signal converted by the time-frequency conversion unit, and is a subcarrier component of the replica signal of the desired signal with respect to the extracted subcarrier component signal. The receiving apparatus according to any one of claims 2 to 4, wherein a subcarrier component adjacent to the subcarrier component is added. The receiving apparatus according to any one of claims 1 to 5, further comprising a plurality of antennas and performing MIMO transmission scheme communication with the transmitting apparatus. The receiving apparatus according to claim 6, wherein the demodulating unit demodulates a signal of each subcarrier component extracted by the restoration unit and performs MIMO separation based on the channel impulse response at the plurality of times. The receiving device is:
A signal of a stream that is a signal sequence transmitted from each of a plurality of antennas included in the transmission device is received as the reception signal,
The restoration unit extracts a subcarrier component of the frequency domain signal converted by the time-frequency conversion unit, and selects a desired subcarrier component of the replica signal of the desired signal for the extracted subcarrier component signal. The receiving apparatus according to claim 7, wherein the stream components are added. The receiving device is:
A signal of a stream that is a signal sequence transmitted from each of a plurality of antennas included in the transmission device is received as the reception signal,
The restoration unit extracts subcarrier components of the frequency domain signal converted by the time-frequency conversion unit, and extracts all of the subcarrier components of the replica signal of the desired signal for the extracted subcarrier component signals. The receiving apparatus according to claim 7, wherein the stream components are added. The demodulator
The receiving apparatus according to claim 7, wherein the signal is demodulated based on a minimum mean square error criterion. In a receiving method for demodulating information from a received signal,
A channel impulse response at a plurality of times in an OFDM symbol interval is estimated, the estimated channel impulse response at a plurality of times is converted into a single channel impulse response, and a time-frequency conversion is performed on the converted channel impulse response. A channel estimation process to estimate the frequency response;
A symbol replica generation process for generating a symbol replica which is a modulation symbol of the demodulated information;
A filtering process for generating a received signal replica that is a received signal replica in a time domain based on the channel impulse response of the plurality of times and the symbol replica;
A subtraction process for subtracting the received signal replica from the received signal;
A time-frequency conversion process of converting the signal subtracted by the subtraction process into a signal in a frequency domain;
A replica signal of a desired signal is generated based on the frequency response and the symbol replica, the replica signal of the desired signal is added to the frequency domain signal converted by the time-frequency conversion process, and each received signal A restoration process for extracting subcarrier components;
A demodulation process for demodulating the signal of each subcarrier component extracted by the restoration process;
A receiving method comprising: A receiver computer that demodulates information from the received signal;
A channel impulse response at a plurality of times in an OFDM symbol interval is estimated, the estimated channel impulse response at a plurality of times is converted into a single channel impulse response, and a time-frequency conversion is performed on the converted channel impulse response. A channel estimation means for estimating a frequency response;
Symbol replica generation means for generating a symbol replica which is a modulation symbol of the demodulated information;
Filter means for generating a received signal replica which is a received signal replica in the time domain based on the channel impulse response of the plurality of times and the symbol replica;
Subtracting means for subtracting the received signal replica from the received signal;
A time-frequency conversion means for converting the signal subtracted by the subtraction means into a signal in the frequency domain;
A replica signal of a desired signal is generated based on the frequency response and the symbol replica, and the replica signal of the desired signal is added to the frequency domain signal converted by the time-frequency conversion means, and each received signal Restoring means for extracting subcarrier components;
Demodulation means for demodulating the signal of each subcarrier component extracted by the restoration means;
Receiving program to function as.

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